Electrical discharge device



May 10y 1938. E; GERMER 2,116,927

ELECTRICAL DISCHARGE DEVICE Filed April 13, 19374 Edmund Ge rmef l INVENTQR Patented May 10, 1.938

lUNITED STATES PATENT OFFICE EC TS Application Aprilia, 1937, serial No. 136,540 In Germany April zo, 1935 2Claims.

This invention relates to electrical discharge devices and to electrodes adapted for use in such devices and to the method of producing and treating such electrodes. More particularly the inven- 5 tion relates to activated solid metallic electrodes and to electrical discharge devices using such electrodes. l

In an application of Hans J. Spanner, Seria tw ,No 'i8'l,986, led August 23, 1929, there is disclosed an activated electrode suitable for electrical discharge devices in which-the electrode is subjected to ionic bombardment and in which, therefore, the activation of the electrode presents l an especially diiiicult problem. It was there dis- 16 closed that in order to meet the requirements of this problem it is advantageousto have the surface of the metallic carrier on which the activation material is deposited as rough as possible. It was suggested in that application to obtain a rough surface by winding fine wire onto a core of heavy wire. It has also been suggested (e. g., in my German application, Serial No. 90,346, filed April 30, 1935) to produce such a surface by mechanically roughening the surface of the metallic carrier, e. g., by groovirlg, milling, etc.

Itis an object of the present invention to provide a metallic carrier in an electrode structure `with a roughened surface especially adapted for carrying activation material. Another object of the invention is to provide electrodes which may be more easilyvactivated, which will have longer life and which in use will have more constant low electrode potential drop.

I have found that these objects can be best attained by an electrical treatment prior to activation.

According to my invention the metallic carrier before the activation treatment may be immersed in an electrolytic bath and subjected to an electrolytic treatment by which it is provided with a spongy metallic surface deposit ina manner well known in the art of electro-metallurgy.

AAlthough I do not claim that such a spongy metallic surface deposit is in itself, unknown to 4l the prior art, it is, so far as Iam aware, unknown to utilize such a deposit in electrodes for discharge devices and especially for holding the activation on the electrodes. VSuch deposits have been known in the art of electro-metallurgy as the 6o result of defective conditions and to be avoided;

but I have now discovered that the result thus produced is superior for the purposes of electrode activation to the surfaces which could be obtained "iin other ways. V 1

one example of my invention a suitable metallic electrode structure (e. ,g., a cylinder for radio tubes, spiral wire or sheet metal, cups, cylinders or discs for gaseousdischarge tubes, etc.) vbefore the application of the activating material is treated in an electrolytic bath. Using, for ex- 5 ample, as the base metallic structure nickel, tungsten or molybdenum, a nickel plating bath is preferably chosen. For best results'the strength of the electrolytic current is chosen so that the Velectrode to be treated is greatly overloaded. 10

Thus, a coating forms on the electrode surface ,which is not a smooth dense plating` but which has a microporous surface (commonly known as nickel sponge, etc.)

After the treatment of the electrode by which 15V this porous surface is produced, it is degassed by heating in vacuum or in an atmosphere of inert gas to drive off any objectionable occluded gases and to reduce any objectionably oxidized ma-` terial; and the activating mass is coated ontp the 20 porous surface; and, finally, the electrode thus coated is again subjected to degassing and/or reduction in vacuo and/or to any other desired ace. g.. to produce successive coatings of different micro-structure and/or of different metals.

Thus, for example, the electrode referred to above after coating with the porous nickel can be subjected to a second chromium plating bath 40 in which the electrode is similarly overloaded so as to produce a micro-porous deposit of chro-` Also the intensity of the current during the treatment may be changed so that the character of the coating is changed throughout its thickf ness. Thus it4 is' particularly advantageous tostart with a Vnormal plating current and gradually to increase the current, thereby increasing gradually the porosity of the applied coating A similar favorable eifect may be attained also if the metal structure to b c treated is connected in the electrolytic bath, not as a` cathode, but as an anode. In this case with a heavy overloading of the electrolytic current the surface of the `dense metal is loosened up so that after the treatment similar favorable effects are4 found. In this way itis possible to treat electrodesin the same bath both at the anode and at the cathode.

As examples of my invention I may take a spiral tungsten wire about approximately 3 mills diameter, e. g.,`of the form shown in li'ig. 1, and connect this as the cathode in aplating circuit and immerse it in a plating'bath containing 227 grams nickel ammonium sulfate, 5'1 grams am-v monium sulfocyanate, 28 grams zinc sulfate, 4.5 liters water and having a strength of about 6 Baum and a temperature of about 27 to 30 C.

This bath may, of course, also contain other ingredients, as is well known in the art of electroplating. As anode a nickel bar is immersed in the bath and connected into the plating circuit.

yThrough this circuit is passed a current of about 0.02 amp. with a voltage of about 1 volt. This current is continued for about l hour after which the electrodeis removed from the bath, dried, placed in the vacuum chamber and heated to a glowing temperature, meanwhile exhausting the vacuum chamber to remove the gases released from the metal. The electrode after cooling, and preferably with little or no exposure to the air, is

immersed in a suspension or paste of 50 parts of barium oxide, 30 parts of strontium oxide and 20 parts of calcium oxide, all in finely divided state and' suspended in a thin solution of collodion. After this dipping, the electrode is dried and may be dipped again or several times with drying V after each. It is then sealed into the tube in which it is to be used and is again subjected to vacuum and heating treatments, e. g., by high frequency bombardment, to decompose the collodioi and drive ofi any occluded gases, and if desired to reduce partially or to any desired extent theactivating oxides; and finally, is subjected to a discharge in the tube, preferably before the final pumping and sealing off of the tube. As a second example, an electrode structure,

' e. g., as shown in any of the figures of the drawing, may be connected into a plating circuit and immersed in an ordinary plating bath, e. g., the nickel plating bath as described in the first example (in which case the electrode structure is itself preferably of nickel), and the plating circuit connected so that the electrode is the a'node in the bath. It is then subjected to a current of approximately 0.05 amp. at 2 volts for a period amaca? of 1 hour. when removed'it win have a desired porous structure and may then be subjected to further treatment substantially as described in connection with the ilrst example.

As another example, the electrode may be treated as in the flrstexample, except that instead of subjecting it to a uniform current throughout its treatment the treatment may be started with a current of 0.015 amp. and increase gradually over a period of 1/2 hour until it reaches a current of 0.25 amp. The treatment may than be continued for Mi hour with said current, after which the electrode is removed and may be subjected to the same cleaning and activation treatmentas before described.

Inthe drawing, I have shown in Fig. 1 a longitudlnal section through a discharge lamp embodying my invention.

In Fig. 2, I have shown in elevation another type of electrode adapted tobe 'directly heated to thermionic temperature by a resistant current and In Fig. 3, I have shown a third type of electrode, namely an indirectly heated uni-potential cathode partly in section and partly in elevation. In all of these guresI have indicated the electrode structure proper or carrier metal bythe reference character i0, I0a, I lb, the lead-in wires by the reference characters II lI ia and IIb; and the porous metal coating with its adhering activation layer, by the reference character I2.--"

What I claim is: l. An electrode for an electric discharge tube -which comprises a dense metal carrier basean integral metallic surface layer thereon, more porous than the base, and a coating of activation material adheringto said porous layer, the outer layer of metal on said electrode being of gradually increasing porosity as the activated surface 

